Hydrocephalus is a neurological condition that is caused by the abnormal accumulation of cerebrospinal fluid (CSF) within the ventricles, or cavities, of the brain. CSF is a clear, colorless fluid that is primarily produced by the choroid plexus and surrounds the brain and spinal cord. CSF constantly circulates through the ventricular system of the brain and is ultimately absorbed into the bloodstream. CSF aids in the protection of the brain and spinal cord. Because CSF keeps the brain and spinal cord buoyant, it acts as a protective cushion or “shock absorber” to prevent injuries to the central nervous system.
Hydrocephalus, which affects children and adults, arises when the normal drainage of CSF in the brain is blocked in some way. Such blockage can be caused by a number of factors, including, for example, genetic predisposition, intraventricular or intracranial hemorrhage, infections such as meningitis, head trauma, or the like. Blockage of the flow of CSF consequently creates an imbalance between the amount of CSF produced by the choroid plexus and the rate at which CSF is absorbed into the bloodstream, thereby increasing pressure on the brain, which causes the ventricles to enlarge.
Hydrocephalus is most often treated by surgically inserting a shunt system that diverts the flow of CSF from the ventricle to another area of the body where the CSF can be absorbed as part of the circulatory system. Shunt systems come in a variety of models, and typically share similar functional components. These components include a ventricular catheter which is introduced through a burr hole in the skull and implanted in the patient's ventricle, a drainage catheter that carries the CSF to its ultimate drainage site, and optionally a flow-control mechanism, e.g., shunt valve, that regulates the one-way flow of CSF from the ventricle to the drainage site to maintain normal pressure within the ventricles. The ventricular catheter typically contains multiple holes or pores positioned along the length of the ventricular catheter to allow the CSF to enter into the shunt system. To facilitate catheter insertion, a removable rigid stylet, situated within the lumen of the ventricular catheter, is used to direct the catheter toward the desired targeted location. Alternatively, or in addition, blunt tip brain cannulas and peel-away sheaths have been used to aid placement of the catheters.
Shunting is considered one of the basic neurosurgical procedures, yet it has the highest complication rate. The most common complication with shunting is obstruction of the system. Although obstruction or clogging may occur at any point along the shunt system, it most frequently occurs at the ventricular end of the shunt system. While there are several ways that the ventricular catheter may become blocked or clogged, obstruction is typically caused by growth of tissue, such as the choroid plexus, around the catheter and into the pores. The pores of the ventricular catheter can also be obstructed by debris, bacteria, or blood clogged in the pores of the catheter. Additionally, problems with the ventricular catheter can arise from overdrainage of the CSF, which can cause the ventricle walls to collapse upon the catheter and block the pores in the catheter wall, thereby preventing CSF drainage.
Some of these problems can be treated by backflushing, which is a process that uses the CSF present in the shunt system to remove the obstructing matter. This process can be ineffective, however, due to the small size of the pores of the ventricular catheter and due to the small amount of flushing liquid available in the shunt system. Other shunt systems have been designed to include a mechanism for flushing the shunt system. For example, some shunt systems include a pumping device within the system which causes fluid in the system to flow with considerable pressure and velocity, thereby flushing the system. As with the process of backflushing, using a built-in mechanism to flush the shunt system can also fail to remove the obstruction due to factors such as the size of the pores and the degree and extent to which the pores have been clogged.
Occluded ventricular catheters can also be repaired by cauterizing the catheter to remove blocking tissue, thereby reopening existing pores that have become occluded. Alternatively, new pores can be created in the catheter. These repairs, however, may be incapable of removing obstructions from the ventricular catheter depending on the location of the clogged pores. Additionally, the extent of tissue growth into and around the catheter can also preclude the creation of additional pores, for example, in situations where the tissue growth covers a substantial portion of the ventricular catheter. Another disadvantage of creating new apertures to repair an occluded ventricular catheter is that this method fails to prevent or reduce the risk of repeated obstructions.
Because attempts at flushing or repairing a blocked ventricular catheter are often futile and ineffective, occlusion is more often treated by replacing the catheter. Although this can be accomplished by simply removing the obstructed catheter from the ventricle, the growth of the choroid plexus and other tissues around the catheter and into the pores can hinder removal and replacement of the catheter. Care must be exercised to avoid damage to the choroid plexus, which can cause severe injury to the patient, such as, for example, hemorrhaging. Not only do these procedures pose a significant risk of injury to the patient, they can also be very costly, especially when shunt obstruction is a recurring problem.
Accordingly, there exists a need for a shunt system that minimizes or eliminates the risk of blockage or obstruction of the catheter pores, and reduces the need for repeated repair and/or replacement, while maintaining the proper CSF level in the brain. Attempts have been made to solve the problems inherent in the shunting process. Some of the prior art is described below.
U.S. Pat. No. 3,669,116 teaches a physiological drainage catheter comprising an elongated tube with a central axis and a peripheral wall surrounding it. A port passes through the wall to the passage for the purpose of draining fluid from the region surrounding the tube. A peripheral cuff surrounds the wall and is fastened thereto on each side of the port, the cuff ballooning away from the wall to leave a cavity therebetween. The cuff is made of a flexible openpore silicone rubber sponge which provides a large number of restricted, but continuous, passages from outside of the cuff to the cavity, and an increased surface area thereby to screen or filter fluid which reaches the port from regions to be drained outside the cuff to minimize clogging, and by its increased surface area to decrease the possibility of being closed by abutment with surrounding tissue.
U.S. Pat. No. 4,593,703 teaches an improvement in design of an implantable telemetric differential pressure sensing device enabling thinner, more compact, and simplified construction for the device; increased pressure sensitivity and range of measurement; and a wider class of applications for such pressure sensing devices in diagnostic medicine and clinical monitoring. The implanted device includes a thin, planar, closed, conductive loop which moves with a flexible diaphragm, the diaphragm moving upon changes in the difference of two bodily pressures on its opposite sides. The position of the conductive loop relative to a resonant circuit fixed in the device determines the resonant frequency of the resonant circuit. The resonant frequency is detected telemetrically outside the body, and its value is used to determine the difference in the two bodily pressures
U.S. Pat. No. 7,025,742 teaches a method that treats a patient for adult-onset dementia of the Alzheimer's type by removing a portion of the patient's cerebrospinal fluid, preferably (although not necessarily) by transporting the fluid to another portion of the patient's body. An apparatus for removing cerebrospinal fluid includes (1) a conduit with a first opening and a second opening, the first opening of the conduit being disposed in fluid communication with a space within a patient's subarachnoid space, the second opening being disposed in fluid communication with another portion of the patient's body; and (2) a flow rate control device attached to the conduit.
U.S. Pat. No. 7,290,454 teaches a differential pressure flow sensor system comprising a disposable flow sensor which has upstream and downstream pressure sensing devices for detecting a differential pressure in a flow channel. Each sensing device comprises a diaphragm, a capacitor and an inductor electrically coupled to the capacitor so as to form an LC tank circuit. The capacitor and/or inductor can be mechanically coupled to the diaphragm such that a deflection of the diaphragm in response to fluid pressure applied thereto causes a change in the resonant frequency of the LC tank. The differential pressure and flow rate can be determined by detecting changes in the resonant frequency using interrogation electronics which can wirelessly interrogate the devices. A calibration capacitor and/or inductor can be formed on each sensing device and trimmed thereon for calibration purposes. Such pressure flow systems can be implemented in medical applications.
US Application 200401487871 teaches an implantable fluid management device, designed to drain excess fluid from a variety of locations in a living host into a second location within the host, such as the bladder of that host. The device may be used to treat ascites, chronic pericardial effusions, normopressure hydrocephalus, hydrocephalus, pulmonary edema, or any fluid collection within the body of a human, or a non-human mammal.
US Application 20040260229 and International Patent Application EP 1491137 teach an implantable medical device that includes a housing, a valve disposed within the housing, a first pressure sensor disposed within the housing upstream of the valve, and a second pressure sensor disposed within the housing downstream of the valve. A CPU is disposed within the housing and is electrically connected to the first pressure sensor and the second pressure sensor. To communicate the measured pressure information to an external device, the CPU compares the pressure measured by the first pressure sensor to the pressure measured by the second pressure sensor and wirelessly communicates these compared pressures to an external device. Alternatively, the CPU may wirelessly communicate the absolute value of the pressure measured by the first pressure sensor and the second pressure sensor to the external device. Additionally, the CPU and sensors may be non-invasively powered using optical or acoustical methods.
US Application 20050113802 teaches a surgically implantable delivery or drainage catheter assembly that includes a porous fiber membrane that is permeable to the intended drainage or delivery fluid, yet has an outer surface morphology and porosity that prevents the ingrowth of tissue. The porous fiber membrane is created using a phase-inversion process which is controlled to select a desired porosity. A reinforcement member is also disposed within the porous fiber membrane.
US Application 20070261496 teaches a biological fluid device that comprises a pressure sensor, which is arranged on the device. The pressure sensor comprises a compressible container, the compression of which is indicative of the pressure, and is capable of wireless communication.
International Patent Application WO/2004/073768 teaches an occlusion resistant medical shunt, particularly a hydrocephalic shunt, that is provided for implantation into a mammal. The shunt has an elongate wall structure configured as a tube having a lumen therethrough and a proximal end for receipt of bodily fluids. The bodily fluids, such as cerebrospinal fluid, flows through the shunt to a distal end for discharge of the bodily fluids. The wall structure of the shunt generally includes a biocompatible medical device material. The shunts of the present invention further include one or more occlusion resistant materials to resist occlusion of the lumenal passage in the shunt.
International Patent Application WO/2006/009467 describes a method for processing pressure signals derived from locations inside or outside a human or animal body or body cavity. Different aspects of the invention relate to a method for optimal differentiating between cardiac beat- and artifact-induced pressure waves, a method for obtaining new and improved information from said pressure signals, and method(s) for predicting pressures inside a body or body cavity from pressure-related signals derivable from outside said body or body cavity. The invention also relates to device(s) and system for sensing continuous pressures signals and displaying output of processing according to the inventive method. Other features of this invention are related to aspects of draining fluid from a brain or spinal fluid cavity.
International Patent Application WO/2007/075349 teaches a differential pressure flow sensor system that comprises a disposable flow sensor which has upstream and downstream pressure sensing devices for detecting a differential pressure in a flow channel. Each sensing device comprises a diaphragm, a capacitor and an inductor electrically coupled to the capacitor so as to form an LC tank circuit. The capacitor and/or inductor can be mechanically coupled to the diaphragm such that a deflection of the diaphragm in response to fluid pressure applied thereto causes a change in the resonant frequency of the LC tank. The differential pressure and flow rate can be determined by detecting changes in the resonant frequency using interrogation electronics which can wirelessly interrogate the devices. A calibration capacitor and/or inductor can be formed on each sensing device and trimmed thereon for calibration purposes. Such pressure flow systems can be implemented in medical applications.
British Patent GB1271361 teaches an apparatus for monitoring the flow of fluid past a surface that comprises a transducer associated with the surface to produce an electric signal representative of the pressure variations due to turbulence, which may be already existing or artificially promoted. For monitoring blood flow in a silastic tube forming part of a dialysis shunt between an artery and a vein, the tube sits in a stirrup part of a body attached by arm to a leaf-spring anchored at one end to a gramophone pick-up arm with a Piezo-electric stylus. The pressure variations in the tube due to turbulence are converted to electrical signals, which are fed to an amplifier and earphones and also rectified and fed to a Schmitt trigger circuit to operate an alarm when the flowrate falls below a predetermined value.
None of the prior art addresses the issues with shunting in as effective a manner as the current invention. The current invention employs three novel shunt technologies for controlling CSF coupled with a pressure/flow sensor that is wireless and implantable. The novel shunt technologies involve an insertion mechanism followed by a two-stage system for reduction of shunt clogging. In the insertion mechanism, the catheter is covered with a removable sheath that prevents clogging of the catheter holes on insertion. In one embodiment, the removable sheath is coated with a substance that will cause particles to adhere to the sheath. The coated sheath is left for an appropriate period of time after insertion of the catheter to remove the removable sheath, so that particulates may settle and the maximum removal effect may be achieved. In the two stage system, the CSF passes through catheter holes that are larger than in typical currently available shunt catheters, and in the second stage passes through a replaceable filter downstream. The current invention decreases invasiveness by employing the filter in an extracranial position, making it relatively easy to remove and replace, as well as easy to monitor and maintain. In addition, a wireless pressure/flow sensor is employed to control flow and CSF fluid levels. The flow sensor is immersible and exhibits reduced vulnerability to pressure and temperature changes and body orientation changes, making it more accurate than flow sensors that have been used in various shunt systems.